The pelorus is a well known navigation instrument for taking the bearing of a sighted object. A relative bearing can be determined with respect to the fore - aft axis of the vessel aboard which the instrument is employed, or pelorus bearing can be provided in conjunction with compass heading to provide a magnetic bearing indication. In order to provide a magnetic bearing of a sighted object by use of conventional instruments, the pelorus and compass readings should be simultaneously made for accurate bearing determination and can require the presence of two individuals for noting the respective bearing and compass heading. A subsequent computation is then required to provide the intended magnetic bearing.